In this next chapter I want to take up the subject of zoonoses. Zoonoses is an infection or an infectious disease that is transmittable under normal and natural conditions from vertebrate animals to humans. It may be enzootic or endemic or epizootic or epidemic. There’s also another term, zooanthroponosis which is a disease transmitted from humans to animals. Now there are different types of transmissions with zoonoses. There is direct transmission, that is intimate contact with an infected animal, a person such as with a bite, a scratch, a spray by infectious urine, contact with fecal material, inhalation of a discharge, respiratory droplets due to coughing or sneezing, airborne spread, this is direct transmission. Then there is indirect transmission where there is an arthropod vector such as a flea, a mite, a mosquito, a tick and fomites such as cockroaches that are contaminated with the particular product going from an animal to a human. Another term we should be familiar with is species jumping. This is the transmission from animals to humans followed by human to human spread and this is the group that we are most interested in. That is, we shall see with HIV/AIDS, with SARS, with flu, that the particular agent went from an animal to a human and then began to spread from human to human. So the first one I’d like to take up is SARS or severe acute respiratory syndrome. If you’ll recall, this completely paralyzed the world a number of years ago because the mortality was quite high from this. Well, it turns out that SARS as we found out much later on was due to a particular virus called the coronavirus which was found in a particular animal called the civet cat which was slaughtered in some of the markets of…of China. But these civet cats had in fact been infected by bats, so it was bats that had the coronavirus, it infected the civet cat, the civet cat when they were killed, the spray of blood, sometimes people inhaled, they got it and they were then able to transmit it to other humans and it led to a type of pneumonia and if you’ll recall there were often pictures such as this from China, which is where the disease particularly had a major impact although it then spread to Honk Kong and Singapore and Canada and to Vietnam and so on. It never became the global pandemic that some of these conditions can become.
This is the latest of pandemics, this is the Ebola virus. Many of you have heard about this. It’s been particularly devastating in West Africa in this recent outbreak but it has occurred in central Africa as well, and let’s take a look at this particular virus which has been considered very contagious thought not very infectious. That is it can spread from one person to another through contaminated feces and blood and so on but doesn’t spread from person to person in a crowded room for example. It doesn’t spread through the aerosol route but rather through the blood and feces and so on of individuals who are infected and sick. They have to be sick with this disease. Here are some of these workers carrying…wearing these gowns to prevent them from having contact with this particular virus. This virus has probably, though we’re not sure, been spread by fruit bats, that is the bats again carry this particular virus. The bats may have contaminated food that was then eaten by an individual and that individual developed this disease, Ebola, and then spread it to other people through their bodily secretions. But it was the bat that originally harbored this virus, and then spread it, gave it to people and it was through the person to person spread that it has taken off. Let’s take a look at another one of these zoonoses. This is one called Nipah virus. Quite interestingly, again, this giant fruit bat and why they harbor these viruses we’re not sure and it’s very uncommon actually, would eat some of the fruit of these trees in Malaysia that were planted in areas where pigs were…pigs were grown. The pigs ate the fruit that fell to the ground and because this fruit was contaminated by the virus, the pig in eating the fruit developed an infection. When these pigs then were taken for slaughter and killed by, in the Abattoirs, the slaughterhouses, the men who were involved in this in the pig killing got the infection from the pig. So it went from a bat to the fruit to the pig to the people who were killing the pigs and up to 250 people about developed or died from this condition, a mortality of around 40% or 50% and this occurred in 1998 and 1999. And to get rid of this particular condition, first of all when the pigs became sick the first thing people did is they took them to market, so oftentimes these sick pigs, and they had developed a pneumonia, were taken to market and people would buy it unsuspecting that this might be this particular condition. And the way that Malaysia eventually got rid of this Nipah virus is they took pigs and they killed them and there is no longer a pig industry in Malaysia where at one time it was quite flourishing. This now takes us up to Bangladesh and in Bangladesh there was also an outbreak of Nipah virus and they couldn’t figure out how did this virus get into the human population. Because there were no pigs in that part of Bangladesh. It was a predominantly Muslim society and pork was not eaten, but they pieced together a story that showed that when these bats went to this date palm juice…now here’s a pot on a palm tree that is collecting date palm juice which is a sort of sweet juice that can also be made into something called gur which is a type of sugar. And when they would lick this because they’re fruit bats and it was very sweet and sometimes they would defecate into the pots. The men who sold this and this date palm juice was considered quite a delicacy would take it from house to house and sometimes this date palm juice was contaminated and individuals who took it would get Nipah infection and the mortality again was around 40% or 50%, sometimes 60%. This was a meningoencephalitis, that is it affected primarily the brain. Here are some bats flying just at dusk and they’re quite large, they have a large wingspan but they only drink fruit and sweet things. So the way to get rid of this was to put a skirt of bamboo over where the…the sap came from the tree into the pot and by doing this you can actually reduce the contamination of the date palm juice because the bat can not have access to that…to that sap that’s coming from the tree. So again a bat to the fruit, contaminating that, humans ingest it and it can spread from one person to another on…only on very, very intimate contact. And this is only through respiratory droplets, so it’s not like someone can walk into a room and cough and others would get it. You have to be extremely close to the individual to get this particular infection. So how do we control the transmission or the introduction of zoonoses? Well, this diagram here shows the linkage between wild EID is emerging infectious diseases, domestic animals and humans. And you can see that they interact. Now I’m not going to go through this entire graph but let’s just take a look at a few of the linkages. The linkage, say between wildlife and domestic animals. Here if domestic animals are closely associated with certain wildlife as we saw with the Nipah virus in Malaysia, there’s a spillover effect and these domestic animals can pick up the infection. If we look then down to the bottom of domestic animals and look at the food processing technology industry, we see that this virus got into humans through the infection in pigs which was then picked up in the slaughterhouses and then in humans it spread from person to person. So we have to break…break a number of these links between wildlife and domestic animals, between domestic animals and humans and even between humans and wildlife and so a lot of the strategies that have been developed to control zoonoses have focused on this type of diagram that we see here. All or most of the new and reemerging diseases, not all, will in fact be related to zoonoses so zoonoses are clearly very, very important and extremely costly. Bovine spongiform encephalitis or mad cow disease costs the U.K. over $9 billion in lost revenue. The Nipah virus which I just talked of cost Malaysia $540 million because of all the slaughter of pigs that had to take place. SARS which we started with cost China upwards of $50 billion because of the lost revenue from trade and tourism and so on and avian flu, H5N1 which we have not covered is going to cost billions and billions of dollars. In fact, another type of flu, H1N1 or what was called unfortunately swine flu, this is just a picture of the economic impact it had in Mexico where this beach would be filled with tourists at a particular time of year and of course it’s empty now because people are afraid and go elsewhere. What I’ve tried to do in this brief time is to talk about the importance of zoonoses. That is the diseases which linked animals to man and how they can spread, how they develop, SARS, Nipah virus are but two examples and there are many, many others. And then how they might be controlled and the economic impact that they can cause. We must be prepared to put much more attention into zoonoses and there is a global program called One Health which is trying to do just that.